This invention relates to benzocoumarin derivatives which are useful as pigments that are primrose yellow to orange in color.
Heavy metal yellow pigments such as lead chromate, cadmium sulfide, and nickel titanate have been widely used in the paint and plastics industry for many years. However, the potential toxicity and environmental problems associated with their production and use has recently caused industry to search for alternatives to these heavy metal pigments.
Organic yellow pigments free from heavy metals provide a possible alternative to the inorganic yellows currently in use. Such alternatives must, however, offer excellent bleedfastness and durability. They also must offer bright intense shades so that they may be extended with a white pigment, such as TiO.sub.2, to obtain needed opacity while retaining the needed color strength. The available organic yellow pigments do not satisfy all of these requirements.
There are six basic types of organic yellow pigments currently in use (Reference: J. Lenoir in "The Chemistry of Synthetic Dyes", Vol. V, K. Venkataramen, Ed., Academic Press, New York, 1971). These are monoazo, diarylide, condensation azo, isoindolinone, anthraquinone, and metal chelate pigments. Each group suffers from one or more disadvantages. Monoazo yellows generally have poor bleedfastness and marginal durability. Diarylide yellows have poor durability. Condensation azo yellows have marginal durability and are expensive to use. Isoindolinone and anthraquinone yellows have relatively low color strength and are expensive to use. Metal chelate yellows are dull, often green pigments which do not completely avoid the heavy metal problem.
The present invention relates to a new class of yellow to orange organic pigments. These new compounds provide bright intense colors which exhibit excellent bleedfastness and durability. They are particularly useful in the pigmentation of paints, plastics, and inks and they offer excellent alternatives to the potentially toxic inorganic pigments currently in use.